Triphenylphosphine oxide

Triphenylphosphine oxide
Names
	Preferred IUPAC name Triphenyl-λ5-phosphanone
	Other names Triphenylphosphine oxide
Identifiers
CAS Number	791-28-6 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	745854
ChEBI	CHEBI:36601 ;
ChEMBL	ChEMBL482091 ;
ChemSpider	12549 ;
ECHA InfoCard	100.011.217
EC Number	212-338-8;
Gmelin Reference	6758
PubChem CID	13097;
RTECS number	SZ1676000;
UNII	Z69161FKI3 ;
CompTox Dashboard (EPA)	DTXSID2022121 ;
	InChI InChI=1S/C18H15OP/c19-20(16-10-4-1-5-11-16,17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15H Key: FIQMHBFVRAXMOP-UHFFFAOYSA-N ; InChI=1/C18H15OP/c19-20(16-10-4-1-5-11-16,17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15H Key: FIQMHBFVRAXMOP-UHFFFAOYAB;
	SMILES O=P(c1ccccc1)(c2ccccc2)c3ccccc3;
Properties
Chemical formula	C18H15OP
Molar mass	278.29 g/mol
Appearance	white crystals
Density	1.212g/cm^3
Melting point	154 to 158 °C (309 to 316 °F; 427 to 431 K)
Boiling point	360 °C (680 °F; 633 K)
Solubility in water	low
Solubility in other solvents	polar organic solvents
Structure
Molecular shape	tetrahedral
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	slight
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H412
Precautionary statements	P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P330, P332+P313, P337+P313, P362, P403+P233, P405
Related compounds
Related compounds	P(C6H5)3S; P(C6H5)3; POCl3; PCl5
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula OP(C₆H₅)₃, also written as Ph₃PO or PPh₃O (Ph = C₆H₅). It is one of the more common phosphine oxides. This colourless crystalline compound is a common but potentially useful waste product in reactions involving triphenylphosphine. It is a popular reagent to induce the crystallizing of chemical compounds.

Structure and properties

Ph₃PO is structurally related to POCl₃.^[2] As established by X-ray crystallography, the geometry around P is tetrahedral, and the P-O distance is 1.48 Å.^[3] Other modifications of Ph₃PO have been found: For example, a monoclinic form crystalizes in the space group P2₁/c with Z = 4 and a = 15.066(1) Å, b = 9.037(2) Å, c = 11.296(3) Å, and β = 98.47(1)°.The orthorhombic modification crystallizes in the space group Pbca with Z = 4 and 29.089(3) Å, b = 9.1347(9), c = 11.261(1) Å.^[4]

The oxygen center is relatively basic. The rigidity of the backbone and the basicity of the oxygen center make this species a popular agent to crystallize otherwise difficult to crystallize molecules. This trick is applicable to molecules that have acidic hydrogen atoms, e.g. phenols.^[5]

As a byproduct of organic synthesis

Ph₃PO is a byproduct of many useful reactions in organic synthesis including the Wittig, Staudinger, and Mitsunobu reactions. It is also formed when PPh₃Cl₂ is employed to convert alcohols into alkyl chlorides:

Ph₃PCl₂ + ROH → Ph₃PO + HCl + RCl

Triphenylphosphine can be regenerated from the oxide by treatment with a variety of deoxygenation agents, such as phosgene or trichlorosilane/triethylamine:^[6]

Ph₃PO + SiHCl₃ → PPh₃ + 1/n (OSiCl₂)_n + HCl

Triphenylphosphine oxide can be difficult to remove from reaction mixtures by means of chromatography. It is poorly soluble in hexane and cold diethyl ether. Trituration or chromatography of crude products with these solvents often leads to a good separation of triphenylphosphine oxide. Its removal is facilitated by conversion to its Mg(II) complex, which is poorly soluble in toluene or dichloromethane and can be filtered off.^[7] An alternative filtration method where ZnCl₂(TPPO)₂ is formed upon addition of ZnCl₂ may be used with more polar solvents such as ethanol, ethyl acetate and tetrahydrofuran.^[8]

Coordination chemistry

Ph₃PO forms a variety of complexes. A representative complex is the tetrahedral species NiCl₂(OPPh₃)₂.^[9]

Ph₃PO is a common impurity in PPh₃. The oxidation of PPh₃ by oxygen, including air, is catalysed by many metal ions:

2 PPh₃ + O₂ → 2 Ph₃PO

References

^ "Triphenylphosphine oxide". pubchem.ncbi.nlm.nih.gov. Retrieved 12 December 2021.
^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.
^ Spek, Anthony L. (1987). "Structure of a Second Monoclinic Polymorph of Triphenylphosphine Oxide". Acta Crystallographica. C43 (6): 1233–1235. Bibcode:1987AcCrC..43.1233S. doi:10.1107/S0108270187092345.
^ Al-Farhan, Khalid A. (1992). "Crystal structure of triphenylphosphine oxide". Journal of Crystallographic and Spectroscopic Research. 22 (6): 687–689. doi:10.1007/BF01160986. S2CID 98335827.
^ M. C. Etter and P. W. Baures (1988). "Triphenylphosphine oxide as a crystallization aid". J. Am. Chem. Soc. 110 (2): 639–640. doi:10.1021/ja00210a076.
^ van Kalkeren, H. A.; van Delft, F. L.; Rutjes, F. P. J. T. (2013). "Organophosphorus Catalysis to Bypass Phosphine Oxide Waste". ChemSusChem. 6 (9): 1615–24. Bibcode:2013ChSCh...6.1615V. doi:10.1002/cssc.201300368. hdl:2066/117145. PMID 24039197.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Patent WO 1998007724. "Process for the preparation of 7-alkoxyalkyl-1,2,4-triazolo[1,5-a] pyrimidine derivatives"
^ Batesky, Donald C.; Goldfogel, Matthew J.; Weix, Daniel J. (2017). "Removal of Triphenylphosphine Oxide by Precipitation with Zinc Chloride in Polar Solvents". The Journal of Organic Chemistry. 82 (19): 9931–9936. doi:10.1021/acs.joc.7b00459. PMC 5634519. PMID 28956444.
^ D. M. L. Goodgame and M. Goodgame (1965). "Near-Infrared Spectra of Some Pseudotetrahedral Complexes of Cobalt (II) and Nickel(II)". Inorg. Chem. 4 (2): 139–143. doi:10.1021/ic50024a002.

[1] "Triphenylphosphine oxide". pubchem.ncbi.nlm.nih.gov. Retrieved 12 December 2021.

[2] D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.

[3] Spek, Anthony L. (1987). "Structure of a Second Monoclinic Polymorph of Triphenylphosphine Oxide". Acta Crystallographica. C43 (6): 1233–1235. Bibcode:1987AcCrC..43.1233S. doi:10.1107/S0108270187092345.

[4] Al-Farhan, Khalid A. (1992). "Crystal structure of triphenylphosphine oxide". Journal of Crystallographic and Spectroscopic Research. 22 (6): 687–689. doi:10.1007/BF01160986. S2CID 98335827.

[5] M. C. Etter and P. W. Baures (1988). "Triphenylphosphine oxide as a crystallization aid". J. Am. Chem. Soc. 110 (2): 639–640. doi:10.1021/ja00210a076.

[6] van Kalkeren, H. A.; van Delft, F. L.; Rutjes, F. P. J. T. (2013). "Organophosphorus Catalysis to Bypass Phosphine Oxide Waste". ChemSusChem. 6 (9): 1615–24. Bibcode:2013ChSCh...6.1615V. doi:10.1002/cssc.201300368. hdl:2066/117145. PMID 24039197.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[7] Patent WO 1998007724. "Process for the preparation of 7-alkoxyalkyl-1,2,4-triazolo[1,5-a] pyrimidine derivatives"

[8] Batesky, Donald C.; Goldfogel, Matthew J.; Weix, Daniel J. (2017). "Removal of Triphenylphosphine Oxide by Precipitation with Zinc Chloride in Polar Solvents". The Journal of Organic Chemistry. 82 (19): 9931–9936. doi:10.1021/acs.joc.7b00459. PMC 5634519. PMID 28956444.

[9] D. M. L. Goodgame and M. Goodgame (1965). "Near-Infrared Spectra of Some Pseudotetrahedral Complexes of Cobalt (II) and Nickel(II)". Inorg. Chem. 4 (2): 139–143. doi:10.1021/ic50024a002.

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